Refrigerator defrosting method and apparatus



F. B. FINK May 25, 1937.

REFRIGERATOR DEFROSTING METHOD AND APPARATUS Filed April 18, 1952 Patented May 25, 1937 REFRIGERATOR DEFROSTING METHOD AND APPARATUS Fred B. Fink, Des Moines,

Kelvinator Corporation, Detroit,

poration of Michigan Iowa, assignor to Mich, a ,cor-

Application April 18, 1932, Serial No. 605,973

An object of my inven method 31 Claims.

tion is to provide a of defrosting a cooling unit and an apparatus of simple, durable and inexpensive construction for performing A further object is to provide a defrosting a cooling unit comprising the method.

method of the circulation of heated fluid through a conduit which is in heat conducting relation the fluid being normally to the cooling unit, cool, but heated for the defrosting operation by an electric heater or the like, an automatic electric switch being provided to control such heating in accordance with an undesirable low temperature condition of or a lower than normal the cooling unit as caused by the accumulation of frost thereon.

A further object is to provide an apparatus and circulating it through the conduit whereby defrosting may be accomplished in a minimum of time with a minimum rise of temperature in the space surrounding the cooling unit.

More particularly, -it is a defrosting apparatus for my object to provide the cooling unit of a refrigerator which consists of afiuid conduit in metallic contact with the cooling unit of a refrigerator and a tank connected therewith, the

conduit and the tank forming a closed fluid circuit for a defrosting fluid.

A further object is to provide heating means for the fluid which can be fluid and to circulate it when defrosting is desired.

Still a further object is to operated to heat the through the conduit provide a defrosting apparatus for a mechanical refrigerator or one in which mechanical means is provided to produce refrigeration motor and to also provide and operated by an electric automatic means for causing the defrosting operation and simultaneously therewith preventing ,any refrigerating operation of the refrigeration mechanism.

A further object is to control the defrosting operation in exact accordance with the temperature condition of a fin or other element of a cooling unit so that defrosting is accomplished when and only when a predetermined thickness of frost has formed on the cooling unit, the

automatic means being operable to discontinue the defrosting operation immediately upon the frost on the cooling unit being substantially melted. The thickness of lates the temperature of frost indirectly reguthe cooling unit by acting as an insulator and thus causing (as it builds up) the refrigeratin g machine to operate longer each running cycle thereof to thereby cause a gradual decrease in the temperature-of the cooling coil to below normal.

With these and other objects in view my invention consists in the construction, arrangement 5 and combination of the various parts of my. method and apparatus, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claims, and illustrated in the accompanying drawing, in which:

Figure 1 is a side elevation of a refrigeration cooling unit and my defrosting apparatus connected therewith, part of the figure being diagrammatic.

Figure 2 is a plan view of the cooling unit 15 and defrosting mechanism, a control switch shown in Figure 1 being omitted.

Figure 3 is a vertical enlarged sectional view on the line 3--3 of Figure 1 showing a. heating means for defrosting fluid.

Figure 4 is a sectional view on the line H of Figure 1 showing the relationship between the defrosting fluid conduit and fins of the cooling unit.

Figure 5 is a sectional view showing my in- 25 vention applied to a jacket type of cooling unit; and

Figure 6 is a sectional view showing it applied to a plate coil type of unit.

On the accompanying drawing, I have used 30 the reference character A to indicate generally the cooling unit of a refrigeration mechanism. The cooling unit A, as illustrated in Figures 1 and 2, comprises a refrigerant conduit I0 and heat absorbing fins l2. A unit of this character 5 is usually mounted in proper position within an insulated room or display case to cool the air therein for thus providing a compartment in which foods especially can be kept from spoiling.

A cooling unit which is cooled by means of 40 mechanical refrigeration accumulates frost and the accumulation is more or less rapid, depending on the moisture condition of the air surrounding the unit. Repeated attempts have been made to provide some form of automatic de- 45 frosting mechanism for cooling units of refrigerators and at present many of them are defrosted by hand which is accomplished by pouring water over the unit and letting it drain oh. This method is both unsatisfactory and inefficient and since it is a hand operation, involves the time of an operator as well as the attendance of someone to observe the condition of the cooling unit so that it can be defrosted whenever necessary. 55

Another way of defrosting a cooling unit isto shut off the refrigeration mechanism and let the compartment in which the cooling unit is mounted gradually rise in temperature whereupon the frost will eventually melt from the unit. This raises the temperature of the food containing compartment however and if the foods, especially meats,. are not removed to some other refrigerator, spoilage may occur.

I have provided a defrosting unit indicated generally by the reference character B which is both automatic and efficient. To make it automatic I provide a control such as the one indicated by the reference character C. a

My defrosting unit B includes a conduit l4 and a tank I 6. The conduit l4 extends from an outlet Ila in the top of the tank I6 to an inlet Mb in the bottom of the tank. The parts are all hard-soldered, brazed, welded or assembled together by suitable pipe fittings or joints in any well known manner so as to form a closed fluid system. I provide a stand pipe l8 extending upwardly from the outlet a for the purpose of providing an air cushion as indicated at 20 in Figure 3.

A suitable cap 22 may be screwed on the top of the stand pipe I! toseal the system after the proper amount of fluid 24 is placed therein to leave the desired space for the air cushion 20. Instead of the cap 22, the upper end of the pipe l8 may be permanently sealed by welding or the like if this is found desirable.

The conduit I4 is in intimate contact with the fins 12 so as to provide a ready path for conducting heat from the fluid 24 and the conduit H to the fins l2 and the refrigerant conduit In. For instance, as shown in Figure 4, the flns l2 and conduit l4 may be soldered or brazed together so that there is a direct metallic path for quick heat conduction. This is an important feature of the invention as will hereinafter become obvious.

I provide a means for heating the defrosting fluid 24 either by heating the exterior of the tank l6, or as shown in Figure 3, utilizing a metal tube 26 inclosing a heating element 28 to heat the fluid by direct contact therewith, the tube 26 being immersed in the fluid. The heating element 28 is preferably of the electric type and of course suitably insulated from the tube Instead of having the tank 16, it is obvious that the ends Ma and Nb of the conduit l4 can be directly connected together and means associated with some part of the conduit to heat the fluid therein.

I have the ends of the conduit l4 connected with the top and bottom of the tank I 6 for the following purpose. Whenever the heating element 28 is energized, it will heat the fluid 24 in the immediate vicinity of the tube 26 and it is well known, of course, that where a portion of a body of fluid is heated, the heated fluid will tend to flow upwardly.

Therefore, soon after the heating element 28 is energized, a circulation of the fluid 24 through the conduit l4 will begin, the direction of circulation being indicated by the arrows 30 in Figure 1. The colder portion of the fluid 24 will then be drawn into the bottom of the tank Hi. This is known as the thermo-syphon principle and by utilizing it, I do not need any mechanical means for circulating the fluid 24, although such means can be provided if found desirable, especially in large installations.

The fluid 24 may be a brine solution because brine does not freeze until a much lower temperature than the freezing point of water is reached. In installations where colder conditions are encountered, however, there might be a tendency for the fluid 24 if it is brine to become slushy and deter proper circulation. In such an installation, fluid with a lower freezing point should be used such as a calcium solution.

From the foregoing description, it will be obvious that I have provided a defrosting unit which when the heating element 28 is energized, will cause circulation of a hot fluid through a conduit which is in heat conducting relation to the cooling unit of a refrigerator. a diffusion of the heat from the fluid 24 to the fins I2 and to the refrigerant conduit H] which is extremely rapid, resulting in melting of the frost on the cooling unit without appreciably raising the temperature of the space surrounding the cooling unit during the defrosting operation. After the frost is all melted, of course, the temperature of such space could be quickly raised by continuing the operation of the defrosting unit, but if the current to the element 28 is shut off just before complete defrosting has occurred the residual heat in the defrosting unit will finish the defrosting operation without raising the temperature of such space and thereby greatest efficiency is obtained.

It is desirable, of course, to control the operation of the defrosting unit automatically so that it needs no personal attention. This can be done by controlling the energization of the heating element 28 in accordance with the temperature of one of the fins 12. As a matter of fact, the temperature of one of the fins in an operating refrigerator becomes lower in proportion to the thickness of the frost thereon because the thicker the frost, the more insulating effect it has on the fin, thereby indirectly causing the refrigeration mechanism to operate longer each cycle of operation to produce the same temperature in the refrigerator in which the cooling unit is mounted. When the fin reaches an undesirable low or a predetermined lower than normal temperature, its temperature can be utilized to operate the control device C to thus automatically control the defrosting unit as will now be described.

The control C comprises a switch box 32 in which is mounted an ordinary refrigerant compressor control switch mechanism C and a special control switch mechanism C for controlling my defrosting unit.

I have shown the two switches combined in one casing as this would be the convenient way to make them, but of course a separate control for the defroster alone could be used and it could be merely hooked into the line in series with the ordinary refrigerant compressor control switch such as C already existing on a refrigerant system.

The control switch C is of the temperature responsive type having a bulb 34 mounted in the food compartment or other portion of the refrigerator so as to automatically maintain the refrigerator at a predetermined temperature. This switch as Well as the switch C" is shown more or less diagrammatic as the specific details do not form any part of my present invention.

Referring to the switch C briefly, a bellows 3G is connected by a tube 38 with the bulb 34. Upon an increase of pressure, as caused by an increase of temperature in the refrigerator, a roller 40 passes center of a cam arm 42 to tip a mercury The result is tube switch 44 to the by an adjusting ,on position. Upon a decrease of temperature, as caused by operation of the refrigerant compressor, the motor of which is shown at, the bellows 36 will be contracted spring 48 for tipping the switch 44 to the off" position. This is the ordinary automatic control for a, refrigerant compressor motor, to keep the temperature of a space in which the cooling unit is mounted between certain predetermined limits.

The switch comprises a bellows 50 connected'by a tube 52-with a bulb 54. The bulb 54 is connected by a clip 56 directly to one of the fins l2 or may be brazed thereto or otherwise related by good temperature conducting connection with a portion of the cooling unit A. The bellows 50 acts upon an arm 58 in opposition to an ad-.- justable spring 60. 64 against'a cam arm 66 on which a double throw mercury tubeswitch G8 is mounted. Upon an increase of temperature, the roller 52 will pass center of the cam arm 66 and tip the switch 68 from the position shown in Figure 1 to an opposite position.

It will be noted that in the position shown, current is being conducted to the heating element 28 and by tracing the wiring, it will be obvious that when the switch is tipped to the opposite position, the heating element28 will be deenergized and the switch C will then be in the normal position for allowing the refrigerant compressormotor 46 to be again energized, depending upon the control switch 0'.

From the foregoing it will be obvious that I have provided means for positively preventing any operation of the refrigerant compressor during the defrosting operation as such operation of the refrigerant compressor would merely be a waste of electricity because of refrigerating and defrosting at the same time.

After the defrosting operation, however, is

completed, the refrigerating operation will be automatically continued in the normal manner.

If it is desired to have defrosting occur at a lower temperature, the adjustable spring 60 can be loosened. The length of the defrosting operation can be determined by adjusting the spring 64 which widens the differential of operation of the switch C" to thus provide a longer period of time between establishing and disconnecting the supply of current to the heating element 28.

The method I have provided for defrosting a cooling coil is very efficient because it only raises the temperature of the cooling fin suflicient to substantially completely defrost it and then is cut off so that residual heat after defrosting is not present. The entire operation is automatic and is accomplished in a minimum of time compared with other defrosting systems.

As far as the apparatus is concerned, it may be applied to different types of cooling units and by way of illustration I have shown a jacket type in Figure 5. In this type there are usually inner and outer walls 10 and 12 between which the refrigerant fluid flows. I have shown a defrosting fluid conduit l which may be of any desired shape but which should be in good heat conducting contact with the'cooling unit.

For instance, it might be a round tube flattened as illustrated and brazed to the wall 12 before the cooling unit is enameled. Thus theenameling will also cover the conduit l5.

In Figure 6 I have shown the plate coil type of cooling unit in which a refrigerant coil ll extends through a metal casing l3, air circulation being provided through the casing. -In this type of A roller 62 is held by a spring unit, frost forms on the outside of the casing l3 and a defrosting fluid channel |5a may be brazed to the casing l3 so that the fluid 24 is in direct contact with the casing. Such direct contact or even the metallic contact illustrated in the prior flgures'provides for readytransmission of heat from the fluid 24 to the parts to be defrosted.

Although I have heretofore in my specification referred to fluid 24 in the conduit I4, I do not wish to be limited to fluid only. Any circulatable medium such as gas or steam could be used instead of fluid. It is well known that steam or gas can be readily circulated and therefore when in hot condition it can be circulated through the conduit l4 for heating the conduit and defrosting the cooling unit.

My method can be somewhat modified, changes may be made in the arrangement and construction of the various parts of my apparatus for practising the method and any suitable circulatable medium can be used without departing from the real spirit and purpose of my invention. I It is,

therefore, my intention to cover by my claims, any modified method or forms of the apparatus or use of mechanical equivalents, which may be included within their scope.

I claim as my invention:

1. The method of defrosting a cooling unit comprising circulating fluid through a conduit which is in heat conducting relation to the cooling unit, heating said fluid to cause such circulation upon an undesirable low temperature condition of said cooling unit being reached, the

commencement of such heating and thereby the control of such circulation being indirectly caused by the accumulation of frost on said cooling unit.

2. Apparatus for defrosting a cooling unit comprising a fluid conduit in heat conducting relation to said'cooling unit, fluid in said conduit, means for heating said fluid and means responsive to a predetermined low temperature condition of the cooling unit to control said means for heating the 3. Apparatus for defrosting a cooling unit comprising a fluid conduit in heat conducting relation to said cooling unit, fluid in said conduit, electric means for heating said fluid and means responsive to a predetermined low temperature of the cooling unit to control the energization of said electric means.

4. Apparatus for defrosting a cooling unit com prising a fluid conduit in heat conducting relation to said cooling unit, fluid in said conduit, electric means for heating said fluid and a switch responsive to a predetermined low temperature of the cooling unit to control the energization of said electric means.

5. Apparatus for defrosting a cooling unit which has mechanical means for reducing the temperature thereof comprising a fluid conduit in heat conducting relation to said cooling unit, fluid in said conduit, means for heating said fluid and automatic means responsive to a predetermined low temperature condition of said cooling unit to render said means for heating the fluid operative and said mechanical means inoperative.

6. Apparatus for defrosting a cooling unit which has electric refrigerating means for reducing the temperature thereof comprising a fluid conduit in heat conducting relation to said cooling unit, fluid in said conduit, electric heater means for heating said fluid and an automatic switch responsive to a predetermined low temperature of the cooling unit to energize said electric heater means and de-energize said electric refrigerating means.

7. Apparatus for defrosting a cooling unit comprising a fluid conduit in heat conducting relation to the cooling unit, fluid in said fluid conduit, means for heating said fluid and settable means responsive to the temperature of said cooling unit to control said means for heating the fluid, said settable means being set for an undesirable low temperature of said cooling unit.

8. Apparatus for defrosting a finned cooling unit comprising a fluid conduit in heat conducting relation to the fins thereof, fluid in said conduit, means for heating said fluid and means responsive to the temperature of said fins to control said means for heating the fluid.

9. The method of defrosting a cooling unit comprising the circulation of heated fluid through a conduit which is in heat conducting relation to the cooling unit and the control of said circulation in direct accordance with the temperature of the cooling unit itself.

10. In a refrigerating system, the method of defrosting the cooling unit thereof which comprises subjecting the cooling unit to a source of heat extraneous of the system and controlling the application of such source of heat in response to an undesirable low temperature of the cooling unit.

11. In a refrigerating system in which frost forms on the cooling unit thereof due to the circulation thereover of the medium cooled thereby, the method of removing the frost from the cooling unit which comprises subjecting the cooling unit to a generated heat and controlling the application of said generated heat in response to an undesirable low temperature of the cooling unit.

12. In a refrigerating system, the method of refrigerating the cooling unit thereof and re moving the frost formed on the cooling unit due to the circulation thereover of the medium cooled thereby, which method comprises circulating a cooling medium through the cooling unit, subjecting the cooling unit to a generated heat and discontinuing the circulation of such cooling medium and controlling the application of generated heat and the circulation of the cooling medium in accordance with the temperature of the cooling unit.

13. Refrigerating apparatus comprising in combination a cooling unit, means for cooling said unit and means for defrosting the cooling unit, said latter means including a source of generated heat and means responsive to an undesirable low temperature of the cooling unit for controlling the application of said generated heat to the cooling unit.

14. Refrigerating apparatus comprising in combination a cooling unit, means for circulating a refrigerating medium through said cooling unit, means for defrosting the cooling unit including an extraneous source of heat and temperature responsive means responsive to a predetermined low temperature of the cooling unit for controlling the application of said source of extraneous heat.

15. Refrigerating apparatus comprising in combination a cooling unit, means for circulating a refrigerating medium through said cooling unit, means for defrosting the cooling unit including an extraneous source of heat and temperature responsive means responsive to a predetermined low temperature of the cooling unit for controlling the application of said source of extraneous heat and being responsive to an increased temperature of the cooling unit for discontinuing the application of the; source of extraneous heat.

16. Refrigerating apparatus comprising in combination a cooling unit, means for circulating a refrigerating medium through said cooling unit, means for defrosting the cooling unit including an extraneous source of heat and means responsive to an undesirable low temperature of the cooling unit for controlling the application of said extraneous source of heat and for rendering the circulating means ineffective.

17. Refrigerating apparatus comprising in combination a cooling unit, mean: for cooling said unit and means for defrosting the cooling unit, said latter means including a source of generated heat and means for controlling the application of said generated heat to the cooling unit, said last means including mechanism responsive to an increased temperature of the cooling unit caused by the application of said generated heat for discontinuing the application of said generated heat.

18. Refrigerating apparatus comprising in combination a cooling unit, means for cooling said unit and means for defrosting the cooling unit, said first means during cooling operation normally operating to cause frost to accumulate on the cooling unit due to the circulation thereover of the medium cooled thereby, said latter means including a source of generated heat and means for controlling the application of generated heat to the cooling unit, said lastmeans including mechanism responsive to an increased temperature of the cooling unit caused by the application of said generated heat for discontinuing the application of generated heat and for restoring the system to normal condition.

19. Refrigerating apparatus comprising in combination a cooling unit, means for circulating a refrigerating medium through the cooling unit, said means normally operating to cause frost to accumulate on the cooling unit due to the circulation thereover of the medium cooled thereby, means for defrosting the cooling unit including an extraneous source of heat and means for controlling the application of said extraneous source of heat to the cooling unit, said last means including mechanism responsive to an increased temperature of the cooling unit caused by the application of said extraneous source of heat for discontinuing the application of said heat.

20. Refrigerating apparatus combination a cooling unit, means for circulating a refrigerating medium through the cooling unit, said means normally operating to cause frost to accumulate on the cooling unit due to the circulation thereover of the medium cooled thereby, means for defrosting the cooling unit including an extraneous source of heat and means for controlling the application of said extraneous source of heat to the cooling unit and for rendering the circulating means ineffective, said last means including mechanism responsive to an increased temperature of the cooling unit caused by the application of said extraneous source of heat for discontinuing the application of said heat and for rendering the circulating means effective.

21. The method of defrosting a cooling unit comprising heating a medium, circulating said medium when heated and which is in heat conducting relation to the cooling unit and controlling comprising in P 2,081,479 such circulation responsive to an undesirable low temperature of the cooling unit.

22. In a refrigerating system, the method of defrosting the coolingunit thereof which comprises externally subjecting the cooling unit to a temperature of greater than 32 F. and controlling the discontinuation of such temperature subjection in response to a predetermined rise in the temperature of the cooling unit caused by such temperature subjection.

23. In a refrigerating system including refrigerating mechanism, the method of defrosting the cooling unit thereof which comprises externally subjecting the cooling unit to a temperature of greater than 32 F. and controlling the discontinuation of such temperature subjection and the starting of said refrigerating mechanism in response to a predetermined rise in the temperature of the cooling unit caused by such temperature subjection.

24QI'he method of defrosting a cooling unit comprising circulating a normally dormant medium through a conduit which is in heat conducting relation to the cooling unit and controlling said circulation only in response to an undesirable low temperature of said cooling unit.

25. The method of defrosting a cooling unit comprising circulating heated fluid through a conduit which is in heat conducting relation to the cooling unit and controlling such circulation in accordance with an undesirable low temperature condition of said cooling unit as indirectly caused by the accumulation of frost thereon.

26. For use with a cooling unit, defrosting apparatus comprising a fluid conduit independent of and in heat conducting relation to said cooling unit, a part thereof being spaced from said unit, fluid in said conduit and electric heating element means for heating said part and thereby the fluid therein.

27. Apparatus for defrosting a cooling unit including a refrigerant conduit and fins thereof comprising a closed defroster conduit independent of said refrigerant conduit and in heat conducting relation to said fins, a circulatable medium in said defroster conduit and means for heating said medium.

28. Apparatus for defrosting a cooling unit comprising a closed fluid conduit in heatconducting relation to said cooling unit, fluid in said conduit, means for heating said fluid and automatic means responsive to undesirable low temperature of the cooling unit for controlling said heating means for heating said fluid only when said means responds to an undesirable low temperature.

29. Apparatus for defrosting a cooling unit including a refrigerant conduit and fins thereof comprising a fluid conduit distinct from said refrigerant conduit and in heat conducting relation to said fins thereof, fluid in said fluid conduit and means for heating said fluid and thereby causing thermo-syphon flow of the fluid through said fluid conduit.

30. Refrigerating apparatus comprising -in combination a cooling unit, means for circulating a refrigerating medium through the cooling unit, means for applying heat to said cooling unit in response to a predetermined frosting of said unit resulting from the circulation thereover of the medium to be cooled and by such application of heat freeing the unit from said frost, and means arranged to render inoperative the heat applying means when the temperature of the cooling unit rises above a frost melting'temperature.

31. In a refrigerating system, the method of defrosting the cooling unit thereof which com prises subjecting the cooling unit to a temperature of greater than 32 Fahrenheit by applying heat thereto, discontinuing refrigeration in said cooling unit, and causing a predetermined rise in temperature of the cooling unit caused by ch heat application to discontinue the latter.

FRED B. FINK. 

